There would be no point of learning Troll if it had no uses. The first, and most obvious, use of Troll is to communicate with trolls! While trolls can be taught simple English, it's much easier to just learn Troll yourself. If you ever come into contact with a troll, your first option should be trying to talk with it. In the case of an aggressive troll, your best bet is doing a quiet, quick grunt followed by a joyful toned roar. This alerts the troll that you are peaceful and you are accepting the troll.
The second use is to introduce the learner to learning new languages. Many more languages are much more complicated than Troll. This means that Troll is a great start for learning new magical languages.
-Henry Ridgeback